Megger SG32-1500M, User Manual

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SG32-UG-EN-V01 Dec 2016
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Methods available on the MTDR100
TDR / Pulse Echo
TDR or Pulse Echo is a low voltage method of fault pre-location suitable for
locating short and open circuits and other faults below approximately 300Ohms.
It is not suitable for high impedance or flashing faults, where HV method should
be used.
Arc Reflection Multi-shot
Arc Reflection Multi-shot is an improved Arc Reflection method which
eliminates the need to set the trigger to the optimum delay time. Its basic
principle is identical to Arc Reflection and is very capable of finding high
resistance, flashing and other faults that can be ignited by a surge generator. A
reference trace is taken without HV present, and then a real-time trace is taken
while applying HV and compared to the reference trace. The HV creates an arc
(flashover) at the fault, which causes a negative reflection of the trace at this
point. The point of divergence between the 2 traces indicates the fault position.
The added advantage of Arc Reflection Multi-shot is to be able to view multiple
traces, all of which have been captured during the period of a single arc. This
removes the need to set the trigger delay to its optimum time as all stages of the
negative reflections of all traces over a certain time interval can be evaluated
.
Differential Arc Reflection (DART)
In Differential Arc Reflection mode unwanted and confusing reflection are
removed leaving a clean trace with only the fault position being displayed by a
positive
pulse (the fault trace is mathematically subtracted from the reference
trace, which turns the initially negative fault reflection into a positive reflection).
This method is especially suited in locating high-resistance faults in complex
cable systems. This differential arc reflection trace (DART) can be displayed at
the same time as Arc Reflection Multi-shot for even better and more confident
fault analysis.
Current Impulse (ICE or Impulse Current)
Impulse Current requires the most interpretation and is therefore not often used;
however it is very suitable for long or wet cables. The fault is ignited and the
resultant transients are recorded by the MTDR, which is acting as a transient
recorder.. The trace displays impulses at both the point of the fault (low
impedance) and also where the surge generator is connected to the cable. Do not
use the first displayed impulse as this includes the “ionization delay” i.e. the time
needed for the fault to flashover. The distance between the impulses is the
distance to fault. For added accuracy try using more than one measurement and
different voltages!